A technology for housing an exothermic composition in a bag having air permeability, which is capable of producing heat by an oxidation reaction of an oxidizable metal, and producing heat in the presence of air, is known (Patent Documents 1 to 3).
Patent Document 1 describes an adhesive exothermic sheet for facial treatment, which includes an exothermic sheet composed of a flat parcel material having air permeability and a powdered exothermic composition included in the parcel material, and an adhesive layer.
Patent Document 2 describes a heating element including an exothermic composition that is capable of producing heat under the presence of air, and a flat parcel material composed of a base material and a coating material, in which the exothermic composition is contained, in which an aeration layer is deposited on one of or both of the above-described base material and the coating material on the side of a surface in contact with the exothermic composition, such that air flows in an interior through the aeration layer from an edge face of the aeration layer on the side of the circumference.
Patent Document 3 describes an air impermeable bag for a heating element that is capable of producing heat under the presence of air, in which an air-impermeable packaging material, which forms the air-impermeable bag for the heating element, is composed of at least a base material film coated with a metallic compound.
Patent Documents 1 and 2 also describe that a polyphosphate is contained in the exothermic composition as a pH adjuster.
Patent Document 3 describes the use of an alkali metal hydroxide and a weakly basic alkali metal salt as a hydrogen generation inhibitor.